This invention relates to a new type of holograms and in particular to holograms in which the holographic image is present in a hydrophilic water-swellable layer.
Holograms wherein the holographic image is present in a hydrophilic water-swellable layer are in general of three main types. In the first of these the photosensitive agent used in the water-swellable layer is a metal dichromate. The binder is usually gelatin in this case and the holograms produced are referred to as dichromated gelatin holograms. Holograms produced using dichromated gelatin yield a very bright holographic image on replay but are very expensive to produce. In the second of these a photopolymerisation mixture is present in the hydrophilic water-swellable layer. After holographic exposure and aqueous processing a hologram is formed in the layer. However hologram produced using this material tend to exhibit low brightness and high haze.
The third type is wherein the photosensitive layer employed is a gelatino silver halide emulsion layer and now this is by far the most common material to employ in the production of holograms. However silver halide sensitised material especially when the hologram is a reflection hologram tends to lack brightness and also to exhibit haze. Thus when the hologram is to be displayed the holographic image is viewed against a black background and if haze or light-scatter is present the black background becomes degraded to a grey background.